There are four standards for wireless local area network, including IEEE802.11, IEEE802.11b; Bluetooth suitable for the frequency band of 2.4 GHz and IEEE802.11a suitable for 5 GHz. When a wireless application electronic device is used for different standards so that a plurality of frequency bands are necessary, the corresponding antenna is used.
Referring to FIG. 1, a perspective view of a prior art dual frequency antennal is illustrated, which is an inverse dual frequency antenna for receiving a first frequency and a second frequency. The antenna 100 has a first plane trans-conductive element 200 and a second plane trans-conductive element 300. The first plane trans-conductive element 200 has an L shape and second plane trans-conductive element 300 has a bended rectangular structure which is vertical to the first plane trans-conductive element 200 and is connected to a joint 400 of the first plane trans-conductive element 200. When the area of the second plane trans-conductive element 300 is overlarge, it will induce the joint to break. However the bandwidth, impedance matching and gain of the antenna 100 are adjustable by the first plane trans-conductive element 200 and the second plane trans-conductive element 300. The area of the second plane trans-conductive element 300 will affect the gain of the antenna. If an antenna with a higher bandwidth is needed, the area of the substrate is needed to be enlarged, which is confined by the installing space. Thus the area of the substrate can not be enlarged effectively.
Therefore, from above description, it is known that the prior art has the following defects.
The prior art is confined by space and thus the bandwidth is confined.
In the prior art, when the second plane trans-conductive element has an overlarge area, it will induce that the joint between the two trans-conductive elements breaks.
In using the prior art, the ability for sensing the harmonics is insufficient and the standing wave ratio is low and thus it will induce the difficulty in the design of the circuit.
The manufacturing process in the prior art is tedious, the cost is high and the installation is difficult.